Abstract
AbstractPMR‐15 is a high‐performance thermoset polyimide resin that is used in many high‐temperature applications. Postcured PMR‐15 produces room‐temperature electron paramagnetic resonance (EPR) spectra from stable freeradical species that are formed during the postcuring stages. The variable‐temperature EPR spectral intensities show a minimum at Tmin in the range −60 to −40°C, and a maximum at Tmax in the range 80–120°C. The EPR intensities follow the inverse temperature dependence of Curie's law below Tmin and are due to a stable free radical. The intensities then increase with increasing temperature between Tmin and Tmax. The free radical with such temperature dependence is not present below Tmin and is undetectable by EPR at temperatures above Tmax. These free radicals are generated during the postcuring process at elevated temperature above 310°C. The thermo‐oxidative degradation involves free radicals generated during the postcuring process in the presence of oxygen gas. © 1993 John Wiley & Sons, Inc.
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